The redistribution of hemopoietic tissue resulting from estrone‐induced osteosclerosis in the mouse was studied. As the marrow was gradually replaced by bone, extramedullary hematopoiesis in the spleen increased at a rate sufficient to maintain hemopoietic homeostasis. The total numbers of colony forming units (CFU) in the tibia and spleen as well as the proportion of CFU in cycle was assessed. After five injections of estrone, tibial CFUs decreased to 2% of control values whereas splenic CFUs increased approximately nine‐fold. The proliferative capacity of the splenic CFU was also increased in the estrone‐treated animals. The increased numbers of splenic CFUs as well as the increased proliferative capacity of this compartment are probably related to the ability of extramedullary hematopoiesis in the spleen to compensate for a marrow that has been replaced by bone.

Platelet-associated IgG (PAIgG) was measured by a simple radial immunodiffusion technique using washed solubilized platelets and commercially available immunoplates. Subjects with normal platelet counts had PAIgG levels of 1.5--7.0 fg/platelet. Subjects with idiopathic immune thrombocytopenic purpura (ITP) had levels ranging from 5.7 to 70.5 fg/platelet. All patients with recurrent ITP and 85% of patients with acute ITP had elevated PAIgg. Elevated PAIgG was also found in 17% of patients with recovered ITP, 40% of patients with SLE and thrombocytopenia, 57% of patients with thrombocytopenia occurring during the course of septicemia, and 100% of patients with IgG myeloma in whom the serum IgG level was clearly elevated, regardless of the platelet count. The results are similar to reports that used more complex techniques.

Defective arythropoiesis characterizes the sideroblastic anemias. The present studies were undertaken to assess the effects of isoniazid, an inhibitor of heme synthesis, on erythropoietin-induced erythroid maturation in hypertransfused mice. Isoniazid was administered at intervals during a wave of induced erythropoiesis, and the effects were assessed in both the bone marrow and peripheral blood. The data showed that isoniazid interfered with heme synthesis and erythroid maturation. The most inhibitory effect of isoniazid was noted at the intermediate normoblast stage. A transient increase in the reticulocyte nonheme iron pool was also found.

SummaryA method for the preparation of standard fibrin clots labeled with radioactive mercury is described. When suspended in aqueous solutions of streptokinase, urokinase and trypsin, the release of radioactivity from the clot is proportionate to the rate of lysis. The per cent of remaining clot measured by the radioactive method and a tyrosine assay is comparable. Hg203 labelled clots are easy to prepare and may be stored for approximately 2 months.

Defective arythropoiesis characterizes the sideroblastic anemias. The present studies were undertaken to assess the effects of isoniazid, an inhibitor of heme synthesis, on erythropoietin-induced erythroid maturation in hypertransfused mice. Isoniazid was administered at intervals during a wave of induced erythropoiesis, and the effects were assessed in both the bone marrow and peripheral blood. The data showed that isoniazid interfered with heme synthesis and erythroid maturation. The most inhibitory effect of isoniazid was noted at the intermediate normoblast stage. A transient increase in the reticulocyte nonheme iron pool was also found.